EVALUATION OF FUNCTIONAL-HETEROGENEITY IN THE CD8 SUBSET WITH T-CELLSFROM T-CELL RECEPTOR-TRANSGENIC MICE

The question of functional differentiation within the CD8 subset has b een addressed in a model of TcR-transgenic (TcR-tg) mice expressing a TcR specific for H-2K(b) (Ti). CD8+ Ti+ T cells present in the periphe ry of these mice have no cytotoxic T lymphocyte (CTL) activity unless they are stimulated with H-2K(b)-expressing cells. In contrast to T ce lls from normal H-2k littermates, alloantigen induction of CTL from Tc R-tg mice is independent of CD4+ T helper (Th) cells and is accompanie d by high level secretion of interleukin-(IL)-2 by Ti+ CD8+ T cells. P recursor frequency analysis performed on CD8+ cells from TcR-tg mice r evealed a high frequency of Th as compared to CTL precursors. This rai sed the possibility of the existence of distinct subpopulations within CD8+ precursors with different requirements for differentiation to fu nctional CTL. FACS analyses (performed on resting and on in vitro stim ulated T cells from normal and TcR-tg mice) demonstrated a heterogeneo us expression of Lv-6C on CD8+ cells with a large enrichment of Ly-6C cells among the Ti+ cells which persisted after stimulation with H-2b cells in conditions that led to a homogeneous expression of the activa tion markers pgp-1 and CD69. The possibility that Ly-6C expression cou ld mark functionally different subpopulations in CD8+ T cells was inve stigated. Stimulation of sorted populations of Ly-6C and Ly-6C+ cells allowed detection of CTL precursors in both these subsets and the majo rity of limiting dilution wells containing one pCTL also scored positi ve for IL-2 secretion. Thus, for CD8+ T cells expressing the same TcR, differentiation led to acquisition of both IL-2 secretion and CTL fun ction and there was no evidence for the existence of a distinct popula tion of helper-dependent CTL precursors.